1. Technical Field
This invention relates generally to medical devices and their method of use. More particularly, this invention relates to prosthetic devices or prosthetic device parts. Specifically, this invention is directed to a cradle, system and method for correctly positioning and orienting a prosthetic device at a surgical site and is most specifically directed to a cradle used to position and orient a final dental prosthesis in a patient's mouth.
2. Background Information
It has become more common in recent years for prosthetic devices and prosthetic device parts to be used to replace missing body parts. These prosthetic devices and parts can take a variety of forms but are generally components which are used to replace damaged or missing parts of the human body and range from devices and parts used to replace soft tissue components to fabricated replacement parts. In this description, all such components will be generally referred to a prosthetic devices but it will be understood that this term should not be narrowly construed to only be limited to particular components.
Prosthetic devices frequently require that very specialized surgery be performed to install the same at a surgical site in the patient's body. One of the issues that arise in these surgeries is that the prosthesis has to be retained in a very particular orientation and position while the specialist is securing the prostheses in place.
By way of example, one of the fields in which this has been an issue is in the installation of dental prostheses, most particularly fixed prostheses. Dentists have been replacing teeth with prosthetic devices, also referred to by the general public as “false teeth”, for many years. When one tooth or a few teeth are missing, it is relatively easy for a dentist or an oral surgeon to have the missing tooth or teeth fabricated and to install the same. (In the rest of this description, the term “dentist” will be used to represent any professional who installs dental prostheses.) One of the prime reasons that this is possible is that the dentist is able to use the remaining teeth as landmarks for positioning and orienting the replacement tooth or teeth. It is far more difficult when the patient is missing all of their teeth on the upper or lower jaw or on both of the upper and lower jaws. This is because there are no fixed or immovable landmarks on that jaw for the dentist to use to correctly position and place the dental prosthetic device.
One of the systems which has been developed to try and aid dental dentists to assist edentulous patients, i.e., patients who are missing entire jaws of teeth, is that invented and marketed by Nobel Biocare AB, of Sweden as the ALL-ON-4® system. This system is covered by a number of patents including but not limited to U.S. Pat. No. 7,950,924 (Brajnovic), U.S. Pat. No. 8,186,999 (Andersson et al), U.S. Pat. No. 8,234,000 (Andersson et al), and U.S. RE43,584 (Andersson et al), the entire specifications of which are incorporated herein by reference.
The system will be described with reference to a patient who has been wearing a non-fixed denture. The non-fixed denture is marked with radio-opaque-markers and, while the patient is wearing the denture, a CT scan (i.e., a computed tomography scan) will be taken of the patient's mouth. The scan will pick up the radio-opaque markers. The non-fixed denture is then scanned by itself in the CT scanner and all of the data from these two scans is fed into a computer. The computer includes programming which analyses the data and generates an exact image of the denture or prosthetic it needs to create to replace the patient's missing teeth. The program allows for manipulation of the image of the scanned jaw and prosthetic so that decisions can be made as to where to place the implants that are necessary for fixing the prosthetic to the patient's jawbone during surgery. The denture shows up on the scan and can be removed or inserted as needed. When the optimum position of the implants is determined, based on the anatomical landmarks of the oral cavity and jawbone visible in the scan, the denture is then inserted back into the image to ensure that optimal anatomical placement of the implants coincides with their optimum placement within the parameters of the prosthetic. This is important to ensure that the implants and any abutments extending therefrom will emerge from the jawbone through the prosthetic in a complementary position. The implant position and angulation is then manipulated on screen to ensure that any abutments will be positioned so that they are hidden behind the teeth on the palatal aspect (upper jaw) and/or lingual aspect (tongue side on the lower jaw).
Once the position of the various components is finalized on the computer, the program generates a parts list and creates the surgical template which is able to deliver this exact placement of the implants and abutments in the patient's mouth. The computer is connected to a manufacturing assembly and it controls the fabrication of a surgical template for the dental prosthetic. In particular, the computer uses the data to generate a milled pattern replica out of a clear composite resin which is identical to the denture relative to the tissue-fitting surface and border extensions. The surgical template is fabricated to the exact specifications determined by the scans. Special holes are drilled into the surgical template during fabrication to indicate the positions at which the implants must be placed to anchor the prosthetic into the patient's jaw. The ALL-ON-4 system made by Nobel Biocare requires only four implants to anchor a fixed prosthetic properly. The implants are meant to be placed into the jawbone in very precise locations and at specific angles that are determined by the computer. The computer also designs the prosthetic and once the implants are installed, the prosthetic is engaged with the implants.
Nobel designed this system with the intention that after the initial scans and production of the surgical template and prosthetic, the actual installation of the fixed prosthetic would be accomplished in a single visit to the dentist's office. But, the system does not function in this fashion in reality. The problem appears to originate in the fact that while the computer is incredibly accurate in creating the surgical template and the final prosthetic, the human dentist is less accurate than the system requires—simply because they are human. When the surgical template is positioned in the patient's mouth, it is seated on the gum tissue. When the dentist drills the hole in the jawbone for any one of the implants, the gum tissue may deform, thereby slightly shifting the location or the angle at which the implant is installed in the jaw. Additionally, implants are designed to be torqued to a very specific tolerance (i.e. they have to be rotated a very specific number of turns). If they are rotated even slightly more than they should be they can be inadvertently countersunk in the jaw. They may also be under-rotated into the jaw, rendering the implant too high. Dentists will also frequently adjust the torque on the implants once the surgical template is removed. Then when the prosthesis is engaged with the implants, it will not be seated properly. When this seating imbalance occurs, too much load is placed on one or more of the implants and they will tend to fail fairly rapidly. At the same time, the fixed prosthesis will not function properly as it will tend to move and put pressure on the patient's jaw.
Because of these problems, the Nobel system is used differently in practice. It has become necessary for the dentist to install the implants and the final fixed prosthetic device in separate visits. In the first visit, the dentist will take all of the necessary CT scans and will send the data to Nobel Biocare for fabrication of the surgical template. In the next visit, the dentist will install the implants in the jaw, attach temporary cylinders to the implants, and then place a temporary denture, also known as a transitional prosthesis, around those cylinders. In this previously known method of installation, as part of the procedure, it is necessary to use pre-fabricated temporary cylinders of uniform size to link the transitional prosthesis to the implants because of the issues with the installation of the implants. When these temporary cylinders are bonded to the transitional prosthesis, they typically have to be cut down so that they are substantially flush with the mouth-facing wall of the transitional prosthesis so as not to potentially injure the patient during use.
Transitional prostheses are typically of fairly poor quality as they are not meant to last more than a few months while ossification of the implants occurs, i.e., while bone grows around the implants. It takes a great deal of time and effort to even install the transitional prosthesis because of the previously mentioned issues with the installation and/or degree of torque of the implants. As a result, it has become commonplace for dentists to hand this job over to dental technicians. A transitional prosthetic is fabricated from acrylic and this components does not include a metal sub-structure. The material used in the transitional prosthesis allows the dental technician to seat, grind, shape, and cut the transitional prosthesis until it fits adequately around the cylinders on the patients' jaw. It can take several hours of time and considerable effort to even get these temporary devices to fit. The patient then has to go away for several months, living with these inferior prostheses while they wait for bone to grow around the implants and secure them in place. Previously known temporary or transitional prostheses are notorious for having poor aesthetics, bite issues causing chewing problems, discomfort and they are known for premature failure during use.
When the patient returns to the dentist for yet another visit, the implants have become embedded in the jaw and the dentist will take a new impression of the patient's jaw and implants. This impression is used to fabricate the final prosthetic device which will fit the actual position of the implants that were previously placed in the patient's jaw. This actual position tends to differ significantly from the original position the computer calculated because the tolerances involved are so tight. The final prosthetic device is comprised of a titanium sub-structure onto which is attached fabricated teeth and a simulated gum. The teeth and simulated gum are fabricated from acrylic or porcelain and are secured to the titanium sub-structure. The titanium sub-structure strengthens the final prosthetic device. After finalizing the design of the prosthetic device, the computer controls the production of the titanium sub-structure. A dental laboratory will typically be utilized to attach the teeth and simulated gum to the sub-structure and then the final prosthetic device is shipped back to the dentist for insertion.
The computer program will also generate a list of the required fixtures and fasteners for securing the transitional prosthesis to the implants and a second list of the required fixtures and fasteners for securing the final prosthesis to the implants. In this previously known system, the various components for the dentist are shipped in at least two shipments. The first shipment includes the surgical template and the implants from Nobel Biocare and the transitional prosthesis from the dental laboratory. The second shipment, which is shipped several months later, includes the final prosthesis and the second group of fixtures and fasteners. It should be noted that the transitional prosthesis has to be substantially altered and modified after implant placement with unpredictable results as previously described. Furthermore, the final prosthesis is only fabricated after a complete round of separate appointments including appointments for taking impressions, bite registration, and trying on of the prosthesis prior to finishing, in order to check aesthetics and bite. The final prosthesis is only then fixed in place by the dentist in a separate final appointment. The entire process from start to finish takes approximately one year to complete.
The above description applies to a guided installation procedure. It is also possible to install a fixed prosthesis using an unguided or freehand installation procedure. In previously known freehand or unguided installations a computer is not utilized to scan a patient's mouth, compile and analyze data accumulated during a scan, nor is a computer used in the fabrication of the surgical template, the transitional prosthesis, or final dental prosthesis. Previously known freehand installations include the following steps. Firstly, the dentist takes an impression of the patient's oral cavity and takes relevant X-rays. The dentist or a dental technician will then make a plaster model from that impression and will craft a surgical template, and a temporary dental prosthesis based on the plaster model. Bite registration, a try-in and X-rays help the dentist determine the best placement of implants and that information will be transferred onto the model in order to correctly position holes on the template and fabricate a transitional prosthesis. The implants are installed using the template and a transitional prosthesis is arduously adapted to temporary cylinders which are screwed to the implants. Several months later after osseointegration, impressions are taken yet again and the final dental prosthesis is fabricated and installed on the osseointegrated implants. While this freehand or unguided procedure works, it takes a substantial amount of labor and time for the patient to finally be fitted with their fixed prosthesis.
There have been many attempts over the last several years to resolve the issues identified above so that the procedure of installing the final prosthesis, as originally conceived, can be accomplished in a single visit to the dentist. None of the fixes proposed in the art have been successful.
There is therefore a need in the art for a device and system which will align the position of the final prosthetic device with the implants in a reliable fashion, thereby simplifying the installation of the final prosthetic device and thus substantially reducing the time and effort required to complete this installation.